The infrared sensilla in the beetle Melanophila acuminata as model for new infrared sensors

Abstract

For the detection of forest fires the "fire-loving" (pyrophilous) jewel beetle <i>Melanophila acuminata </i>uses a pair of sensor arrays each consisting of about 90 infrared (IR) receptors which are located on either sides of the body. The IR receptors most likely have evolved from common contact hair mechanoreceptors. Compared to a mechanoreceptor, an IR receptor shows the following special features: (i) the formation of a complex cuticular sphere instead of the bristle; the sphere consists of a hard outer exocuticular shell as well as of an inner softer and spongy mesocuticular core. (ii) The enclosure of the dendritic tip of the mechanosensitive neuron inside the sphere in a fluid-filled inner pressure chamber which is connected with the system of microcavities and nanocanals in the mesocuticular core. Hence we propose that an IR sensillum most probably acts as a microfluidic converter of infrared radiation into an increase in internal pressure inside the sphere which is measured by the mechanosensitive neuron. Because the miniaturized receptors respond within a few milliseconds to a brief pulse of IR radiation an approach is made to develop technical IR sensors based on the <i>Melanophila</i> IR receptors. Numerical simulations of sensor performance suggest that the sensitivity of a single IR receptor is in the range of 15 mW/cm². Theoretical calculations which are based on a hypothetical fire of defined temperature and size demonstrate that a beetle should be able to detect a forest fire from a distance of 10 km. A fluidfilled Golay cell was taken as a basis for the design of a first sensor prototype.